1. Field of the Invention
The present invention relates to a multi-beam laser scanner that comprises a plurality of lasers. In particular, the invention relates to a multi-beam laser scanner that further comprises an automatic power control (APC) system which automatically controls the power of the laser.
2. Description of the Related Art
A plurality of laser diodes in the multi-beam laser scanner are arrayed in the sub (vertical) scanning direction, so that a plurality of lines can be simultaneously scanned while the main (horizontal) scanning is carried out. Therefore, the multi-beam laser scanner has the advantage of swift scanning. In general, the laser scanner is provided with an APC circuit in order to maintain stable gray levels of the patterns to be formed, since the gray levels of patterns are affected by deterioration or fluctuation of the light emitted from the laser diode. The APC circuit controls the emission power of the laser diode by feeding back signals from a photo diode that monitors light emission from the laser diode. For a multi-beam laser scanner provided with the APC circuit, the automatic power control operation (APC) should be performed for each individual laser diode.
In recent years, a photo diode integrated laser diode, in which a laser diode and a photo diode are integrated in a package, and a multi-laser diode, in which a plurality of laser diodes and a single or a plurality of photo diodes are integrated, have been provided.
However, in general, the number of photo diodes in the multi-laser diode is less than the number of laser diodes mounted in a multi-laser diode, hence the photo diodes in the multi-laser diode cannot detect the beams from each of the laser diodes independently. Therefore, for monitoring the laser power of each laser diode independently, a plurality of photo diodes and light guide structures are necessarily provided external to the multi-laser diode and the built-in photo diodes of the multi-laser diode are not used. Consequently, the scanning apparatus with the multi-laser diode requires intricate structures.
An object of the present invention is to provide a multi-beam laser scanner in which real-time automatic power control is individually available for each laser by using a photo diode which monitors the plurality of lasers.
According to the present invention, a laser power control circuit utilized in a laser scanner that comprises a plurality of lasers for forming a latent image on a photosensitive member by scanning the plurality of lasers is provided. The laser power control circuit comprises a photo-detecting member and a laser power control processor.
The photo-detecting member simultaneously receives laser beams emitted from each of the lasers and outputs an output signal in response to the received laser power. The laser power control processor controls the laser emitting power of each laser for each time period which is assigned to each of the lasers. Further the laser emitting power is controlled in accordance with the output signal from the photo-detecting member.
According to the present invention, a laser scanner is provided that comprises a photosensitive member, a laser power control circuit a photo-detecting member and a laser power control processor.
The photosensitive member is for forming a latent image. The laser power control circuit comprises a plurality of lasers for forming the latent image on the photosensitive member by scanning the plurality of lasers. The photo-detecting member simultaneously receives laser beams emitted from each of the lasers and outputs an output signal which responds to received laser power. The laser power control processor controls the laser emitting power of each laser for each time period which is assigned to each laser. The laser emitting power is controlled in accordance with the output signal from the photo-detecting member.